Tow cable termination

ABSTRACT

A specialist tow cable termination for sustaining the tensile load when an object is towed at high speeds at the end of an cable behind an aircraft, the termination comprises a closed eye bolt attached to the cable and a U-bolt looped through the eye bolt attached to the object. The arrangement allows significant pivoting bending stresses to the tow cable.

This invention relates to a tow cable termination for sustaining thetensile load when an object is towed at high speeds at the end of acable, in particular to a termination used to connect a tow cable to anelectronic warfare decoy used in fast jet applications for protectionagainst missile attack.

One technique used to protect jet aircraft against missile attack is anelectronic decoy, which is towed behind the aircraft by a cable. Due tothe high performance of these aircraft and the significant trailingvortices created by the aircraft wings, particularly during high “G”manoeuvres, the method by which the cable is terminated and connected tothe decoy is fundamental to the successful operation of the towed decoy.The cable termination has to transmit those forces acting on the decoyin flight (aerodynamic drag and inertia) into tow cable.

The decoy's flight performance follows from its aerodynamic design,which to a large extent is determined by the relative positions of thecentres of pressure and mass of the decoy. With a highly stable decoy,the decoy's centre of mass follows the tow cable, so that the cabletermination transmits the loads from the decoy to the cable with littleoff-axis deviation. However, with a less stable decoy, or in a very highvortex environment or during high “G” manoeuvres, the axis of the decoycan fluctuate or deviate significantly with respect to the axis of thecable, typically up to a cone angle of plus or minus 90 degrees. Inthese circumstances, either the cable termination has to flex over thisextremely wide angle of movement, or the tip of the tow cable itself hasto flex over this range. Modern materials such as Kevlar (Kevlar is atrademark of El Dupont de Nemours and company) have a very high strengthto weight ratio and therefore are ideal for use as tow cables. However,even such modern materials cannot sustain local bending in a highlydynamic environment, and the rapid and persistent flexure of the cablenear to the cable termination in a high vortex environment can lead tocatastrophic failure. Specialist cable terminations have been proposed,but these generally have a limited angle of articulation, typically lessthan a cone angle of plus or minus 30 degrees. Techniques to relievecable strain, to compensate for this low articulation, have been used,but these methods are insufficiently robust significantly to extend thelife of the cable/cable termination arrangement. A low angle ofarticulation at the cable termination results in the tow cable flexingnear the tip of the cable, resulting in the failure of the tow cable andthe loss of the decoy. This mode of failure places a severe restrictionon the flight envelope of the aircraft when towing a decoy.

Accordingly, the present invention provides a tow cable termination forsustaining the tensile load when an object is towed at high speeds atthe end of a cable, the termination comprising a closed eye boltattached to the cable and a U-bolt looped through the eye bolt andattached to the object.

Such an arrangement enables a high degree of articulation, up to a coneangle of plus or minus 90 degrees, whilst easily being capable ofsustaining the normal tensile loads sustained when a fast jet aircraftis towing a decoy and of transmitting these loads into the tow cablewithout also transmitting any of the lateral forces which would causethe cable to flex.

Preferably the U-bolt is attached to the object so as to protrude fromthe object. This is an important factor in enabling the articulation;because the linkage is outside the envelope of the towed object(typically a decoy radome) the motion of the linkage is not restrictedby the object itself impinging on the linkage.

The cable termination may comprise a cable barrel mounted to the end ofthe cable, the eye bolt being releasably attachable to the cable barrel.The cable barrel is the main interface to the tow cable. Within thiscomponent there may be features which enable the cable to be fixed by aconventional resin potting process so as to form a joint having astrength equivalent to that of the tow cable. Another desirable featureof the cable barrel is that it enables the optical and electricalconductors to be split out of the cable structure and routed to thedecoy for connection to the electronics systems therein. In this case itis advantageous for the eye bolt to have an aperture for allowing atleast part of the cable to extend through to connect to the object.Thus, the electronic and other systems in a decoy can be connected tothe aircraft without the connection having to sustain any tensile loadscaused by towing the decoy.

The cable barrel and the eye bolt are preferably provided with matchingscrew threads, so as to be releasably attachable. The aperture in theeye bolt allows optical and/or electrical conductors running down thecore of the cable to connect through to the tow decoy. Due to the highdynamic motion and loads experienced on the eye bolt and the U-boltwhere these are now looped together, one or both are preferably coatedwith a low friction material (such as by electroplating with a lowfriction coating) to enable the two elements to move freely as theyarticulate (pivot) in flight.

The U-bolt is preferably adapted to connect to an interface piece withinthe towed object so as to connect the U-bolt to the object and to permitpivotable motion therebetween. The design of the U-bolt and theinterface piece is such as to minimise bending moments and fatiguestresses. The interface piece provides mechanical support to the U-bolt,by ensuring the structure is closed around the two arms of the U-bolt tothe greatest extent possible whilst still maintaining the requiredkinematic motion. It is also important to maintain the minimum length ofU-bolt commensurate with the degree of articulation required.Accordingly the U-bolt may be threaded at the ends and attached to theobject by nuts threaded thereonto. This arrangement allows the length ofU-bolt protruding from the object to be adjusted easily. Preferably theexterior of the interface and the interior of the object have matchingsliding surfaces, such as spherical surfaces, to permit slidingtherebetween, thus permitting a certain amount of pivotable motionwhilst providing a firm mounting. Integral with the interface betweenthe object and the interface piece may be environment seals to preventthe ingress of water and dust.

The invention will now be described by way of example only and withreference to the accompanying FIG. 1, which shows an exploded view of atow cable termination assembly in accordance with the present invention.

The assembly shown in FIG. 1 comprises four main components forconnection to the tow cable (not shown, but in use would be on the lefthand side of the assembly shown in the drawing). The first component isthe cable barrel 1 which is the main interface to the tow cable (notshown). The cable barrel 1 is in the form of a hollow cylinder which isconnected to the cable by a convention resin potting process, forming ajoint having a strength equivalent to that of the cable itself. Part ofthe exterior surface of the cable barrel 1 (the right hand portion asshown in the FIGURE) has a screw thread adapted to engage with amatching screw thread on the interior of eye bolt 3.

Eye bolt 3 is part of the articulation linkage; it is a high strengthcomponent and has an internal screw thread to accept the cable barrel 1.At one end (to the right as shown in the drawing) the eye bolt has aclosed link (preferably circular) which mates with the U-bolt 5. Eyebolt 3 has an aperture (not shown) allowing optical and electricalconductors in the cable (not shown) to exit the eye bolt for connectingwith the systems internally of the object to be towed.

The eye bolt 5 is secured to the object to be towed (illustrated here byradome 9) by interface piece 7 and nuts 11. The legs of U-bolt 5 arethreaded for engagement with nuts 11, which hold interface piece 7against the interior surface of radome 9. Interface piece 7 hasspherical exterior surface adapted to engage with a matching surface onthe inside of radome 9 so as to allow a certain amount of slidingmovement so that the radome can pivot (although the main articulationtakes place where the U-bolt 5 is looped through eye bolt 3).

In use, as the cable and cable barrel 1 are towed through the air atfast jet speeds and the towed object 9 is buffeted and forced tooscillate by the trailing vortices from the towing aircraft, the towedobject 9 pivots relative to the eye bolt 3 thus minimising the amount ofstress applied to the tow cable itself.

Although described in connection with an object being towed through theair, the principles of the invention apply equally to objects beingtowed through water, for example to sonar decoys.

1.-9. (canceled)
 10. A tow cable termination for a towed decoy that is towed at high speeds at the end of a cable, the termination comprising a high articulation arrangement including a closed eye bolt attached to the cable and a U-bolt attached to the towed decoy and looped through the eye bolt, the eye bolt having an aperture for receiving conductors in the cable and for allowing routing of the conductors through the articulation arrangement to systems within the towed decoy.
 11. A termination as claimed in claim 10, wherein the U-bolt is attached to the towed decoy so as to protrude from the towed decoy.
 12. A termination as claimed in claim 11, comprising a cable barrel mounted to the end of the cable, the eye bolt being releasably attachable to the cable barrel.
 13. A termination as claimed in claim 12, comprising an interface piece adapted to connect the U-bolt to the towed decoy and to permit pivotal motion therebetween.
 14. A termination as claimed in claim 13, wherein the exterior of the interface piece and the interior of the towed decoy have matching spherical sliding surfaces which permit sliding therebetween.
 15. A termination as claimed in claim 14, comprising seals between the towed decoy and the interface piece for preventing water and/or dust ingress.
 16. A termination as claimed in claim 15, wherein the U-bolt is threaded at the ends and attached to the towed decoy by nuts threaded there onto.
 17. A termination as claimed in claim 16, wherein the eye bolt and/or the U-bolt is/are coated with a low friction material.
 18. A termination as claimed in claim 10, comprising a cable barrel mounted to the end of the cable, the eye bolt being releasably attachable to the cable barrel.
 19. A termination as claimed in claim 18, comprising an interface piece adapted to connect the U-bolt to the towed decoy and to permit pivotal motion therebetween.
 20. A termination as claimed in claim 19, wherein the exterior of the interface piece and the interior of the towed decoy have matching spherical sliding surfaces which permit sliding therebetween.
 21. A termination as claimed in claim 20, comprising seals between the towed decoy and the interface piece for preventing water and/or dust ingress.
 22. A termination as claimed in claim 10, comprising an interface piece adapted to connect the U-bolt to the towed decoy and to permit pivotal motion therebetween.
 23. A termination as claimed in claim 22, wherein the exterior of the interface piece and the interior of the towed decoy have matching spherical sliding surfaces which permit sliding therebetween.
 24. A termination as claimed in claim 22, comprising seals between the towed decoy and the interface piece for preventing water and/or dust ingress.
 25. A termination as claimed in claim 10, wherein the U-bolt is threaded at the ends and attached to the towed decoy by nuts threaded there onto.
 26. A termination as claimed in claim 10, wherein the eye bolt and/or the U-bolt is/are coated with a low friction material. 